"It's a tough, tight, smaller thriller, in a way, about the underworld in Boston. Irish gangsters and the police," said Scorsese, who hasn't seen Infernal Affairs. "Based on a Chinese film, apparently, but very unique in and of itself."

Scorsese was initally wary of doing another gangster movie "but the nature of the game that's played between the characters, whether they're police or gangsters, and the following through of each character to their ultimate fate is fascinating to me."

DiCaprio added that in the film "I'm going undercover to be with the gangster. It's certainly a great chess game &#Array; one crooked cop, one semi-good cop who infiltrates the Mob underworld. I'm looking very much forward to it."